1. Field of the Invention
The present invention relates to a shadow mask and, more particularly, to a two-layer shadow mask for forming electronic elements on a substrate.
2. Description of Related Art
Active matrix backplanes are widely used in flat panel displays for routing signals to pixels of the display in order to produce viewable pictures. Presently, active matrix backplanes for flat panel displays are formed by a photolithography manufacturing process, which has been driven in the market by the demand for higher and higher resolution displays, which is not otherwise possible with other manufacturing processes. Photolithography is a pattern definition technique which uses electromagnetic radiation, such as ultraviolet (UV) radiation, to expose a layer of resist that is deposited on the surface of a substrate. Exemplary photolithography processing steps to produce an active matrix backplane include coat photoresist, pre-bake, soak, bake, align/expose, develop, rinse, bake, deposit layer, lift off photoresist, scrub/rinse, and dry. As can be seen, the active matrix backplane fabrication process includes numerous deposition and etching steps in order to define appropriate patterns of the backplane.
Because of the number of steps required to form an active matrix backplane with the photolithography manufacturing process, foundries of adequate capacity for volume production of backplanes are very expensive. An exemplary partial list of equipment needed for manufacturing active matrix backplanes includes glass-handling equipment, wet/dry strip equipment, glass-cleaning equipment, wet clean equipment, plasma chemical vapor deposition (CVD) equipment, laser equipment, crystallization equipment, sputtering equipment, ion implant equipment, resist coater equipment, resist stripping equipment, developer equipment, particle inspection equipment, exposure systems, array filet/repair equipment, dry etch systems, anti-electrostatic discharge equipment, wet etch system, and a clean oven. Furthermore, because of the nature of the active matrix backplane fabrication process, the foregoing equipment must be utilized in a class one or class ten clean room. In addition, because of the amount of equipment needed and the size of each piece of equipment, the clean room must have a relatively large area, which can be relatively expensive.
Alternatively, a vapor deposition shadow mask process is well known and has been used for years in microelectronics manufacturing. The vapor deposition shadow mask process is a significantly less costly and less complex manufacturing process, compared to the photolithography process; however, the achievable resolution of, for example, an active matrix backplane formed via shadow mask technology, is limited. Publications disclosing vapor deposition shadow mask processes as well as related processes are disclosed in U.S. Patent Application Publication No. 2003/0193285; U.S. Patent Application Publication No. 2002/0011785; U.S. Pat. Nos. 6,384,529; and 4,919,749.
Presently, shadow mask manufacturing techniques are not favored due to the lack of sufficiently high resolution to meet today's demand for high resolution products, such as active matrix backplanes. As a result, photolithography manufacturing techniques continue to be utilized to produce such high resolution products.
Moreover, the vapor deposition shadow mask process has other certain limitations that are well recognized in the industry. For example, the minimum aperture size that can be produced accurately within a shadow mask is dependent upon several factors, such as the thickness of the shadow mask and the overall area of the shadow mask, as is well known by those skilled in the art. More specifically, the larger the area of the shadow mask, the thicker the shadow mask must be in order to maintain strength and structural integrity during handling and use. However, the thicker the material of the shadow mask, the more difficult it is to achieve highly accurate and small apertures. As a result, the capability to achieve small microelectronics dimensions and, thus, high resolution, by use of the vapor deposition shadow mask process is limited by factors, such as the thickness and overall area of the shadow mask.
Therefore, what is needed, and not disclosed in the art, is a method and apparatus for improving the resolution of a vapor deposition shadow mask process thereby extending its use in manufacturing, especially the manufacturing of high resolution flat panel displays. Still other needs will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.